Bottom Line:
Inhibitory neurons make up a substantial fraction of the neurons in the preBötzinger complex (preBötC), a site that is critical for mammalian eupneic breathing.Inspiratory-phase photoinhibition in Arch-transfected mice during inspiration increased tidal volume without altering inspiratory duration, whereas expiratory-phase photoinhibition shortened the latency until the next inspiration.We conclude that glycinergic preBötC neurons modulate inspiratory pattern and are important for reflex apneas, but that the rhythm can persist after substantial dampening of their activity.

Affiliation: Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, California, USA.

ABSTRACTInhibitory neurons make up a substantial fraction of the neurons in the preBötzinger complex (preBötC), a site that is critical for mammalian eupneic breathing. We investigated the role of glycinergic preBötC neurons in respiratory rhythmogenesis in mice using optogenetically targeted excitation and inhibition. Channelrhodopsin-2 (ChR2) or Archaerhodopsin (Arch) were expressed in glycinergic preBötC neurons of glycine transporter 2 (Glyt2, also known as Slc6a5)-Cre mice. In ChR2-transfected mice, brief inspiratory-phase bilateral photostimulation targeting the preBötC prematurely terminated inspiration, whereas expiratory-phase photostimulation delayed the onset of the next inspiration. Prolonged photostimulation produced apneas lasting as long as the light pulse. Inspiratory-phase photoinhibition in Arch-transfected mice during inspiration increased tidal volume without altering inspiratory duration, whereas expiratory-phase photoinhibition shortened the latency until the next inspiration. During persistent apneas, prolonged photoinhibition restored rhythmic breathing. We conclude that glycinergic preBötC neurons modulate inspiratory pattern and are important for reflex apneas, but that the rhythm can persist after substantial dampening of their activity.

Mentions:
A critical role of inhibition in the preBötC in controlling respiratory pattern is likely in the production of apneas10, such as during swallowing or breathholding. To determine whether preBötC GlyT2 neurons participate in generating apneas, we photoinhibited these neurons during Breuer-Hering lung inflation reflex (BHIR)-induced apneas10. The lungs were inflated with sufficient continuous positive airway pressure (CPAP) to produce apneas that lasted ~11 s (~4 cm H2O) during control periods (Fig. 5a, top). Photoinhibiting Arch-transfected preBötC GlyT2 neurons (1 s pulse) broke the apnea with one or two breaths (Fig. 5a, bottom; n = 3). Laser onset at 5.5 ± 0.5 s after onset of CPAP (CPAP + Laser) induced a first breath at 5.8 ± 0.5 s, i.e., a 300 ms delay from the laser onset versus an expected first breath at 11.8 ± 1.4 s during control (CPAP only) periods (ANOVA; P = 3×10−6; Fig. 5b; n = 3).

Bottom Line:
Inhibitory neurons make up a substantial fraction of the neurons in the preBötzinger complex (preBötC), a site that is critical for mammalian eupneic breathing.Inspiratory-phase photoinhibition in Arch-transfected mice during inspiration increased tidal volume without altering inspiratory duration, whereas expiratory-phase photoinhibition shortened the latency until the next inspiration.We conclude that glycinergic preBötC neurons modulate inspiratory pattern and are important for reflex apneas, but that the rhythm can persist after substantial dampening of their activity.

Affiliation:
Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, California, USA.

ABSTRACTInhibitory neurons make up a substantial fraction of the neurons in the preBötzinger complex (preBötC), a site that is critical for mammalian eupneic breathing. We investigated the role of glycinergic preBötC neurons in respiratory rhythmogenesis in mice using optogenetically targeted excitation and inhibition. Channelrhodopsin-2 (ChR2) or Archaerhodopsin (Arch) were expressed in glycinergic preBötC neurons of glycine transporter 2 (Glyt2, also known as Slc6a5)-Cre mice. In ChR2-transfected mice, brief inspiratory-phase bilateral photostimulation targeting the preBötC prematurely terminated inspiration, whereas expiratory-phase photostimulation delayed the onset of the next inspiration. Prolonged photostimulation produced apneas lasting as long as the light pulse. Inspiratory-phase photoinhibition in Arch-transfected mice during inspiration increased tidal volume without altering inspiratory duration, whereas expiratory-phase photoinhibition shortened the latency until the next inspiration. During persistent apneas, prolonged photoinhibition restored rhythmic breathing. We conclude that glycinergic preBötC neurons modulate inspiratory pattern and are important for reflex apneas, but that the rhythm can persist after substantial dampening of their activity.